Device for exploring an underground formation crossed by a horizontal well comprising several sensors permanently coupled with the wall

ABSTRACT

The invention relates to a device for exploring an underground formation crossed by a well, suited to work in well portions where the advance thereof under the effect of gravity is difficult, notably in horizontal well portions or in well portions greatly inclined to the vertical. A plurality of rigid exploration modules (Mi) are interconnected end to end, each one including a rigid pipe (1), a flexible leaf (11) fastened to each pipe (1) so as to press against the wall of the well at least one box (18) containing sensitive elements, a linking cable (32) connected to a surface central station (40), and a connecting block (26) comprising an acquisition system (37) connected to the various modules (M1-Mn) by a bundle of electric conductors running through the tubular elements (1), and a deferred electric connection useful in damp conditions between linking cable (32) and the acquisition system. The connecting block is interposed between the array of exploration modules (M1-Mn) and a rigid string (39) connected to the surface operating device (38) for driving the exploration assembly into the well portion. The invention may be used for seismic prospecting for example.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for exploring an undergroundformation crossed by a well, suited to work in well portions where theadvance thereof under the effect of gravity is difficult, notably inhorizontal well portions or well portions greatly inclined to thevertical.

2. Description of the Prior Art

According to a well-known technique, seismic exploration of a geologicformation is performed by placing a receiving and/or transmitting set inone or more wells drilled through the formation in order to pick upsignals reflected by subsoil discontinuities in response to seismic oracoustic waves emitted in a well or at the ground surface.

Seismic equipments can be used in vertical portions or in sufficientlyvertical portions of the wells and, in this case, they are loweredtherein through the effect of gravity.

Seismic equipments are for example placed in a well tool or in severalwell tools arranged in series along an electrical cable, as describedfor example in the assignee's Patents: French Patent 2,501,380 andcorresponding U.S. Pat. No. 4,428,422, French Patent 2,616,230 andcorresponding U.S. Pat. No. 4,901,289, French Patent 2,636,741 andcorresponding U.S. Ser. No. 410,417.

The assignee's patents French Patent 2,656,034 and corresponding U.S.Pat. No. 5,181,565 and French Patent 2,674,029 and corresponding U.S.Pat. No. 5,243,562 describe a method of seismic prospecting of ageologic formation comprising using a reception device including one ormore reception units that are set in a vertical well by means of aproduction string. The units are driven to the setting depth thereof andpressed against the wall of the well or against a casing pipe. Couplingcan be achieved by means of shoes or arms that can be driven away fromthe string under the action of springs. These units can also be placedin boxes that are driven away from the string and mechanically decoupledtherefrom.

The assignee's French Patent 2,703,470 and U.S. Ser. No. 219,268describe a process for setting, in one or more wells crossing anunderground zone, a seismic or acoustic wave transmission-receptiondevice comprising for example transmitting-receiving transducers thatcan be placed behind a tubular string used for other purposes andconnected, permanently or not, to a surface control and recordingstation by means of cables. Such an assembly allows for example toperform P-wave or S-wave loggings of the layers surrounding each welland therefore a long-lasting monitoring of a reservoir.

The assignee's French Patent 2,655,373 and corresponding U.S. Pat. No.5,111,880 describe a system for driving a non rigid exploration deviceincluding several sondes connected together by electrical cable portionsinto a well where the advance thereof under the effect of gravity ishindered notably because of the inclination of the well to the vertical.This device is guided towards a deflected well zone by means of atubular string of pipes. A deferred electrical connection device is usedto connect the array of sondes to a cable connected to a surface controland recording station. A fluid current is established in the string inorder to push the first sonde out of the string and to allow opening ofthe anchor arm. A traction exerted on the string allows the array ofsondes to be taken out of the well and measurement cycles are conducted.

SUMMARY OF THE INVENTION

The invention is notably suited for subsurface seismic prospectingoperations.

The device according to the invention allows exploration of anunderground formation crossed by a well and it is suited to be loweredinto a well zone where the advance thereof under the effect of gravityis difficult, notably in a well portion greatly inclined to thevertical. The invention comprises:

a plurality of rigid exploration modules interconnected end to end, eachone comprising a rigid tubular element provided, at each end thereof,with a connection with at least one other tubular element, at least onebox containing sensitive elements, a spring spacer for pressing each boxpermanently against the wall of the well, and decoupling device forisolating mechanically each box from the tubular elements,

a linking cable connected to a surface central station; and

a connecting block comprising an acquisition system connected to thevarious modules by a bundle of electrical conductors running through thetubular elements, connected to the sensitive elements, for collectingsignals coming from the various sensitive elements, a deferredelectrical connection useful for wet conditions between the linkingcable and the acquisition system, the connecting block being interposedbetween the exploration modules and a rigid string connected to surfaceoperating device for driving the exploration assembly into the wellportion.

According to an embodiment, the spring spacer comprises for exampleflexible leaves, each one resting at the ends thereof on sleeves securedto each tubular element, to which the boxes are fastened, and thedecoupling device comprises sheaths made from a damping material,interposed between each flexible leaf and the corresponding tubularelement.

Each sleeve includes for example a supporting element set between twoend stops secured to the tubular element, and is mechanically isolated,by means of a sheath, from the supporting element and the stops. Thedevice comprises electric connectors inside the rigid tubular elementsfor electric connection with the bundle of electric conductorsassociated with the sensitive elements.

Each supporting element can comprise, for example, two parts on eitherside of the tubular element, the sheath being interposed, and fasteningmeans for joining the two parts and optionally an indexing device forpreventing any rotation of the supporting elements with respect to thetubular element.

Each flexible leaf is preferably secured, at the ends thereof, to pinsthat can move in guide ports in plates secured to each supportingelement.

According to another embodiment, the spring spacer comprises flexibleleaves to which the boxes are fastened, each flexible leaf fitting intoa slot provided in the wall of the pipe along a generating line andresting, at the opposite ends thereof, on sleeves secured to a rigidtube placed inside each tubular element, the decoupling device includessheaths made from a damping material, interposed between each sleeve soas to insulate it acoustically from the inner wall of the tublar elementand from the rigid tube, and each flexible leaf is secured, at the endsthereof, to pins that can move in guide ports provided in the sleeves.

According to another embodiment, the deferred electric connectionincludes a multi-contact plug, a tubular extension for guiding, in theconnecting block, a multi-contact socket connected to themulti-conductor cable and a lock for locking the socket in an engagingposition.

According to a particular embodiment, the device comprises a tubularhead element including an unbalanced mass and an orientation indicatorfor determining the angular positioning of the whole of the explorationmodules with respect to the vertical.

The device according to the invention is advantageous in that:

it can be made by interconnecting end to end a variable number ofstandard exploration modules associated, by means of a connecting block,with a string of pipes that is of sufficient length to be pushed downinto a well portion that is either very inclined or so shaped that itprevents free lowering of the array of modules,

the electrical links between the various instruments or sensors are alljoined and protected in the tubular elements.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the device according to the inventionwill be clear from reading the description hereafter of embodimentsgiven by way of non limitative examples, with reference to theaccompanying drawings in which:

FIG. 1 diagrammatically shows a first embodiment of the invention, setin a well part of which is horizontal,

FIG. 2 diagrammatically shows a sectional view of the layout of eachexploration module;

FIG. 3 shows in detail the layout of a connecting sleeve of a flexibleleaf;

FIG. 4 diagrammatically shows the mode of connection, to a bundle ofconductors running along the tubular elements, of the electricalconductors associated with the sensitive elements;

FIG. 5 diagrammatically shows a sectional view of a block connecting allof the exploration modules to a string of pipes extending up to thesurface; and

FIG. 6 shows a second embodiment comprising two flexible leavesassociated with the tubular elements by means of fastening means placedinside these elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention includes (FIGS. 1, 2) of an array of modules M1, Mi, Mi+1,. . . , Mn interconnected end to end. Each one of these modules Miincludes a rigid tubular element or pipe 1 having at the two oppositeends thereof a fastening piece 2 in order to be connected (by screwingon for example) to the ends of the adjacent tubular elements. Twosleeves 3 are arranged on each pipe 1 at a distance from one another.Each sleeve 3 comprises a supporting element 4 placed between two endstops 5 and 6 rigidly fastened to pipe 1. A sheath made from an elasticmaterial 7 is placed around the tubular element between each pair ofstops 5 and 6. Supporting elements 4 each comprise two half-shells 4a,4b pressed against sheath 7 on either side of the tubular element andjoined to each other by screws 8. In order to prevent rotation ofsupporting elements 4 around pipes 1, at least one of stops 5 and 6comprises an indexing dowel 9 which fits into a corresponding cavity ofone of the half-shells, 4a for example. The decoupling sheaths 7comprise end plates 10 for isolating mechanically supporting elements 4from the respective stops thereof 5, 6.

The device also comprises a flexible leaf 11 having at the opposite endsan end piece 12 provided with a cavity for a pin 13 (FIGS. 2, 3). Adecoupling device 14 of the "silent block" type for example is arrangedaround each pin 13. One of the half-shells 4a of each supporting element4 comprises two lateral plates 15 oriented parallel to the axis of thepipes and provided with elongate openings 16 for guiding the pin 13 ofeach end piece. Sliding of each pin 13 provides each flexible leaf 11with a certain bending latitude. The opposite half-shell 4b of eachsupporting element 4 comprises a bearing shoe 17.

A box 18 intended for exploration instruments is fastened to the medianpart of each flexible leaf 11 (FIG. 2). These instruments may be sensorsnotably sensitive to acoustic or seismic waves such as a triaxialgeophone or "triphone" 19 for example. The electrical conductors 20associated with these instruments run out of boxes 18 through sealedducts (not shown) and run along flexible leaf 11. They enter pipe 1through an opening (not shown) at the level of one of the supportingelements 4.

A multi-pin connector 20a (FIG. 4) is placed inside each pipe 1. It isaccessible by removing a detachable plate 21 covering an opening throughthe wall. Electrical conductors 22 associated with the instruments inthe box 18 of the same module Mi on the one hand, and conductors 23associated with other instruments in the next modules Mi+1. . . Mn onthe other are welded to the pins of connector 20.

The whole of the modules, interconnected end to end, have a tubular headelement 24 at a first end provided with an unbalanced mass and with anorientation indicator (not shown) intended to determine the orientationof the unbalanced mass with respect to the vertical plane. An indicatorof a well-known type comprising a pendular weight in contact with apotentiometer track can for example be used.

At the opposite end thereof, tubular element M1 is connected by a pipe25 to a connecting block 26 provided with a deferred electricalconnection useful in wet conditions. Block 26 comprises (FIG. 5) atubular body 27, a multi-contact plug 28 oriented along the axis of body27, in the center of a tubular guide extension 29 whose section issmaller than that of the body and ends at a flange 30. This extension 29serves to guide a multi-contact socket 31 that is connected to thevarious conductors of a multi-conductor cable 32 which fits onto plug28. Socket 31 have a tubular weighting bar 33. Locks 34, which can beremote-controlled from the surface, allow the socket to be locked in aposition of plugging onto plug 28.

A cable 35 connects multi-contact plug 28 to a sealed compartment 36 ofthe tubular body 27 containing an acquisition and transmission system 37as described for example in the assignee's French Patent 2,688,896.Connecting block 26 is connected to surface operating device 38 by meansof a string of pipes 39.

System 37 receives the signals transmitted thereto through a bundleformed by adding successively, at the level of connectors 21, theconductors coming respectively from the various boxes 18 associated withthe array of modules M1 to Mn and with the orientation indicator in thetubular head element 24. System 37 digitizes received signals and codesthem in order to be transmitted to a surface central control andrecording station 40.

In order to simplify the set up of exploration modules M1-Mn, they canbe standardized by placing preferably in each one of them identicalmulti-pin connectors 21 with a sufficient number of pins in order toallow interconnection of all the conducting lines that finally end atacquisition and coding assembly 37.

According to a layout described in the assignee's French Patent2,547,861, connection between the multi-conductor cable 32 and thecentral station 40 is facilitated by using a special side-entry sub 41allowing, once it is in place, changing of the length of the string ofpipes 39 without it being necessary to interrupt the conducting links.

An exploration assembly comprising 12 tubular elements 1 having a lengthof multiples of ten meters, made of steel, aluminium or glass fiber,associated each with a "triphone", and containing for example anelectric connector 20 with 61 pins also allowing electric connection ofthe orientation indicator in head section 24, can for example be set up.

Operation

Setting the array of exploration modules M1 to Mn in a zone of a wellwhere operations are planned is performed as follows:

The tubular head element 24 is introduced into the well, as well as, bysuccessive interconnections end to end, the various modules M1 to Mn,the pipe 25, the connecting block 26 and possibly a certain number ofsections of the string of pipes 39. The special side-entry sub 41, inwhich the multi-contact socket 31 having weighting bar 33, is inserted,is fastened thereafter. A swivel (not shown) is thereafter associatedwith the string of pipes 39 in order to pump multi-contact socket 31until it fits onto the plug 28 of connecting block 26.

A sufficient number of sections is then added to the string of pipes 39so as to drive the array of exploration modules M1-Mn into the zone ofthe well where exploration operations are to be performed. Bymonitoring, from surface station 40, the indications of the orientationdetector in the head element 24 provided with a weighting mass and byrotating sufficiently the string of pipes 39 during the advance thereof,the various modules M1 to Mn can be so oriented that the flexible leaves11 and thus the instrument boxes 18 are all in the same plane, thevertical plane for example.

A seismic source can for example be placed on the surface or in anotherwell, seismic pick-ups are placed in the boxes 18 of the various modulesM, and transmission-reception cycles can be carried out while thesignals collected by acquisition set 26 and transmitted through cable 32are recorded at the surface station 40.

The whole of the modules can be shifted at will by adding (or byremoving) additional sections to the string of pipes 39 so as to explorethe formation over a greater well length and to perform multiplecoverages.

In the first embodiment described above, each exploration modulecomprises a single flexible leaf 11 for pressing an instrument boxagainst the wall of the well, and a diametrically opposite bearing shoe17. However, exploration modules M1-Mn possibly including severalflexible leaves optionally bearing other instrument boxes 18 can ofcourse be used.

This is notably the case with the embodiment of FIG. 6 having twoflexible leaves 11 each equipped with a box for exploration elementssuch as geophones for example. The device comprises a rigid tube 41whose diameter is smaller than that of each tubular element 1 and thatis placed inside the latter. It is held in position, in relation to thetubular element, by two sleeves 42. An elastic sheath 43 is placedaround each sleeve 42 so as to decouple it acoustically from both tube41 and the inner wall of tubular element 1. The flexible leaves 11 arepartly fitted into grooves 44 provided along two opposite generatinglines of each tubular element 1. The pins 13, at the opposite endsthereof, can slide in the guide ports 45 provided in end pieces 42. Withthis fastening mode, each tubular element offers protection to theconnecting sleeves of the flexible leaves when the device progressesalong the well.

An additional section comprising a source of acoustic or seismic wavescan also be associated with the array of exploration modules M1-Mn, ortransmitting-receiving transducers can be placed in boxes 18 withoutdeparting from the scope of the invention.

The following modifications may also be provided without departing fromthe scope of the invention:

the flexible leaves allowing coupling of the instrument boxes with thewall of the well may be replaced by other coupling means such as shoesconnected to arms opened by action of spacing devices;

the single acquisition system 37 may be replaced by electronicacquisition modules distributed in various tubular elements 1 andcommunicating the signals acquired to a coding and transmission assemblyin connecting block 26;

the rigid tubular elements may be replaced by semi-rigid multi-conductorcable elements with an external glass fiber sheath;

the separate mechanical and electric connectors 2 and 20A of FIG. 4 maybe replaced by a combined embodiment where the mechanical connection ofthe tubular elements leads to the fitting of the electrical connectors,as described for example in the assignee's patent EP-290,338;

tubular elements 1 are provided, according to a known technique, withslots intended to reduce the propagation velocity of the waves along thestring may be used.

I claim:
 1. An exploration device to be driven in a well through anunderground formation to a portion deviating from a vertical orientationthereof by securing the device to an end of a pipe string made byinterconnection end to end of pipe sections, the device including:aplurality of rigid exploration modules interconnected end to end, beingdisposed at least partially in the portion and each having a rigidtubular element provided, at each end thereof, with a connection forconnection with at least one other tubular element, at least one box, atleast one sensor housed in the box, a spring spacing device for pressingeach box against a wall of the well, and a decoupler for mechanicallyisolating each box from the tubular elements; a first multi-conductorcable connected to a surface central station; and a connecting blockincluding an acquisition and transmission electronic system foracquisition of signals sensed by the different sensors and transmissionthereof to the central station, a second multi-conductor cable runningthrough each tubular element, for connecting each sensor in each box tothe connecting block and a connector for making connections in a wetenvironment and connecting the first multiconductor cable with theconnecting block when the exploration modules are lowered in the well.2. An exploration device to be driven in a well through an undergroundformation to a portion deviating from a vertical orientation by securingthe device to an end of a pipe string made interconnection end to end ofpipe sections, the device including:a plurality of rigid explorationmodules interconnected end to end, each having a rigid tubular elementprovided at each end thereof, with a connection for connection with atleast one other tubular element, a sleeve secured to each tubularelement, at least one box, at least one sensor housed in the box, aflexible leaf for pressing each box against a wall of the well, each ofthe leaves resting at the end thereof on the sleeves, and a decouplerfor mechanically isolating each box from the tubular elements, thedecoupler including a sheath made from a damping material interposedbetween each flexible leaf and one tubular element; a firstmulti-conductor cable connected to a surface central station; aconnecting block including an acquisition and transmission electronicsystem for acquisition of signals sensed by the different sensors andtransmission thereof to the central station, a second multi-conductorcable running through the tubular elements, for connecting each sensorin each box, to the connecting block and a connector for makingconnections in a wet environment connecting the first multiconductorcable with the connecting block when the exploration modules are loweredin the well.
 3. A device as claimed in claim 2, wherein each sleevecomprises a supporting element placed between two end stops secured toone tubular element and mechanically isolated by the sheath from thesupporting element and the two end stops and further comprisingelectrical connectors inside the rigid tubular elements for electricalconnection to the second multi-conductor cable.
 4. A device as claimedin claim 3, wherein each supporting element comprises two parts disposedon either side of a tubular element with the sheath being interposedbetween the two parts and one of the tubular elements and furtherincluding a fastener for joining the two parts.
 5. A device as claimedin claim 3 further comprising an indexer for preventing rotation of eachsupporting element with respect to each tubular element.
 6. A device asclaimed in claim 4 further comprising an indexer for preventing rotationof each supporting element with respect to each tubular element.
 7. Adevice as claimed in claim 2, wherein each flexible leaf is secured, atends thereof, to pins movable in guide ports provided in plates securedto each supporting element.
 8. A device as claimed in claim 3, whereineach flexible leaf is secured, at ends thereof, to pins movable in guideports provided in plates secured to each supporting element.
 9. A deviceas claimed in claim 4, wherein each flexible leaf is secured, at endsthereof, to pins movable in guide ports provided in plates secured toeach supporting element.
 10. A device as claimed in claim 5, whereineach flexible leaf is secured, at ends thereof, to pins movable in guideports provided in plates secured to each supporting element.
 11. Adevice as claimed in claim 1 further including a rigid tube arrangedinside each tubular element, a flexible leaf for pressing each boxagainst a wall of the well and sleeves secured to the decoupler, eachsleeve being provided with guide ports, wherein a wall of each tubularelement is provided with slots and each one of the flexible leaves fitsinto one slot and rests at opposite ends, the sleeves each including asheath made from a damping material, interposed between each sleeve andthe tubular element for acoustically decoupling an inner wall of thetubular element and the rigid tube, and each flexible leaf is secured,at the ends thereof, to pins movable guide ports.
 12. A device asclaimed in claim 2 further including a rigid tube arranged inside eachtubular element, a flexible leaf for pressing each box against a wall ofthe well and sleeves secured to the decoupler, each sleeve beingprovided with guide ports, wherein a wall of each tubular element isprovided with slots and each one of the flexible leaves fits into oneslot and rests at opposite ends, the sleeves each including a sheathmade from a damping material, interposed between each sleeve and thetubular element for acoustically decoupling an inner wall of the tubularelement and the rigid tube, and each flexible leaf is secured, at theends thereof, to pins movable guide ports.
 13. A device as claimed inclaim 1, wherein the wet comprises a multi-contact plug, a tubularextension for guiding a multi-contact socket connected to the secondmulti-conductor cable in the connecting block and a lock for locking thesocket in an engaged position.
 14. A device as claimed in claim 2,wherein the wet comprises a multi-contact plug, a tubular extension forguiding a multi-contact socket connected to the second multi-conductorcable in the connecting block and a lock for locking the socket in anengaged position.
 15. A device as claimed in claim 1, further comprisinga tubular head element including an unbalanced weight and an orientationindicator for determining an angular position of the plurality ofexploration modules with respect to a vertical orientation.
 16. A deviceas claimed in claim 2, further comprising a tubular head elementincluding an unbalanced weight and an orientation indicator fordetermining an angular position of the plurality of exploration moduleswith respect to a vertical orientation.
 17. A device as claimed in claim1, wherein the pipe string comprises a side-entry sub allowing passageof the first multi-conductor cable.
 18. A device as claimed in claim 2,wherein the pipe string comprises a side-entry sub allowing passage ofthe first multi-conductor cable.
 19. A device in accordance with claim1, wherein the spring spacing device is an elongated member whichdeforms elastically.